Typically, in order to control emissions of nitrogen oxides (NOx), recent automobiles are furnished with an EGR. The typical EGR system recirculates a part of the exhaust gas into an intake line so that the combustion temperature at a cylinder of an engine is lowered. For example, Japanese patent publication No. 2003-97369 discloses an intake device comprising an intake manifold in which an EGR passage is integrally formed, whereby increasing the mechanical strength of the intake device. According to another example, Japanese patent publication No. 2003-328864 discloses an EGR device comprising a double layered heat exchanger that is provided with a heating passage at the center thereof and a cooling passage at the outer circumference. According to yet another example, Japanese patent publication No. 2000-291455 discloses an EGR system furnished with cooling fins for cooling the recirculated exhaust gas.
The EGR system according to the prior art typically comprises EGR pipes for recirculating a part of the exhaust gas into an intake manifold, a valve for controlling the recirculated exhaust gas, a cooler, and a distributor disposed in the intake manifold so as to supply the recirculated exhaust gas to each of cylinders, respectively. The cooler serves to decrease the temperature of the recirculated exhaust gas. Typically, the cooler comprises a cylindrical housing, a plurality of pipes installed into the housing, a chamber formed in the housing, and a coolant pipe. Another EGR system employs a plate-type distributor formed by combining two plate members, so that the mechanical complexity is significantly reduced.
However, such EGR systems are disadvantageous in that the cooler results in an increase in the number of components and mechanical complexity of the system. Furthermore, the EGR systems are disadvantageous because the systems require sophisticated work in connecting the coolant pipe to the EGR distributor. Because the recirculated exhaust gas is supplied to the cylinders through a pipe, to which each cylinder is connected in series, the amount of exhaust gas recirculated to each cylinder is not uniformly distributed. Due to the unregulated distribution of the recirculated exhaust gas, the efficiency of the EGR system is lowered.